I had a bunch of ideas on how things worked and quickly discovered things were even more genius when I was actually able to see it in person. You guys are very close to understanding how the back platform stows and deploys. Photos can't do it justice. I'll make a video of it one day.
(STOWAGE INSTRUCTIONS located on interior wall)
The STAIRS, RAILING, and SIDE PLATFORM are stored ahead of the Shelter and aft of the Cab. I wondered how the square platform could be held in place at either of the side shelter doors with stairs alone. Well it turns out, it can't. That is where the hanging rods come into play. Look aft of the railing in the pic above, and note the rectangular pinned door on the long enclosure.
These RODS support the side door's platform (square stored platform in storage in pic above, between shelter and cab) by attaching to the platform and then attaching to the recessed hanging points located just left and right of upper side doors.
Now to address the AFT PLATFORM and how it deploys. Someone above, correctly stated that it has connection points that slide within the vertical rails to the left and right of the dual doors. There are a couple pins that lock the stowed floor in place as you see it above here. All these ladders and porches are light aluminum. No steel. So they are amazingly light, but sturdy. Its easy for anyone to carry any single stairs or platform by themselves.
The way this large platform/porch deploys downward is by first unpinning it, pulling out the center I-BEAM support (with the black star on it) as this is the piece that holds the two side supports in a locked position towards the truck. Then deploy the left and right support arms. These all provide the physical support for the porch in it's deployed position. Below is a photo showing the armored version of this truck and the square porch is actually being used as landing at the bottom of the stairs to likely support the stairs in the soft sand (preventing damage to shelter attachments) and to double as a shoe debris remover.
Now one or two people simply grab the bottom edge of the stowed platform and pull out and towards you. The top two sliders attached to the porch in inlayed into the vertical track will gently slide down and the entire porch is in place. Now you simply add the stairs to the porch and attach the railing. There is steel cabled flexible railing to attach to the porch to protect anyone from falling off the porch. There are attachment points to further attach the larger set of stairs and a handrail.
Inside the side stowage boxes, in addition to this flexible railing, are ground support stands that go into position not beneath the slide-outs, but the sides of the truck frame. They ONLY provide support to preventing the lateral rolling that would occur if multiple people were inside working and walking back and forth...because that is what it was designed to do.
Showing the flexible railing on platform/porch.
Showing square platform/porch as landing pad for starboard stairs. Also can see one of the vertical supports which keeps the truck from rocking.
Slide out can be cranked out/extended or retracted back in with the hand crank you see sticking out just below bottom left of porch. The I-Beam it penetrates allows for the handle to crank them out/in while stowed. Zach with "Bantha" uses a power drill to do this labor. The military used 19 year old privates. Very simple and robust mechanism.